Fibers and filaments that have an active functionality when connected to an energy source have been included in textile yarns. Such functional fibers and filaments can include electrically conductive metallic wires or stainless steel fibers for the purpose of conducting electrical current, transmitting signals or data, shielding from electromagnetic fields or electrical heating. In addition, metallic or electrically conductive surface coatings can be applied onto yarns for these same purposes. Such functional fibers and filaments can also include optical fibers for the purpose of providing data or light transmission, or acting as deformation sensors. Such fibers and composite yarns including such fibers or coatings have been fabricated into fabrics, garments, and apparel articles.
There is a perceived need for textile yarns that have a high level functionality when connected to an energy source (sometimes referred to as “smart electronic textiles”). Smart electronic textiles include those textiles in which the textile itself can provide the elements of a classical electronic circuit, which can be delivered through the textile structural elements, i.e. yarns. Depending on the integration complexity, such textile yarns can provide an advanced embedded and active functionality into the textile and can thus allow the textile to act as a truly integrated electronic structure. Textile yarns for so-called “smart electronic textiles” can include at least one material that acts (a) as a passive component (for example, a resistor, inductor, or capacitor), (b) as an energy source (for example, a battery), (c) as a semiconductor device (for example, a diode or transistor), or (d) as a transducer (for example, a photovoltaic or light emitting material).
In this regard, FiCom, a European Union funded project within the Information Society Technologies research program, is working to integrate computing ability directly into fibers that can then be woven into textile products. FiCom's efforts have focused on embedding the basic unit of computation, the transistor, into fibers that may then be connected to form inverters, gates, and higher level circuits (F. Clemens, et al., “Computing Fibers: A novel fiber for Intelligent Fabrics?”, Advanced Engineering Materials 2003, vol. 5, No. 9, pp. 682) (“Clemens”). FiCom seeks different processes to develop new substrates in fiber form that are suitable for semiconductor processing. One such process, disclosed in WO 03/021679 A2 (to A. Mathewson, et al.), includes a first step involving forming transistors on special silicon-on-insulator (SOI) substrates according to conventional techniques, followed by extraction of long thin membrane polycrystalline silicon fibers from the wafer substrate using standard etching techniques. This technique provides short planar fibers that are limited by the wafer surface (of length of about 42 mm and cross section of 35×1 μm) and can be difficult to handle.
A second process, disclosed in Clemens, involves, in a first step, producing pure continuous SiO2 and SiC fibers via a ceramic powder extrusion technique, followed by sintering to yield polycrystalline SiC fibers and pure amorphous SiO2 glass fibers. Although continuous filaments can be produced by this process based on inherently semiconductive materials, integrating electronic functionality on such a curved surface currently requires a complex process that has yet to be demonstrated along the length of the fiber. Further, the Clemens and Mathewson approaches are based on traditional silicon semiconductor manufacturing processes, which may present further limitations with regard to cost, process scalability, and complexity of the electronic functionalities that can be achieved. In addition, the mechanical characteristics of the resulting fibers may fail to possess desired textile characteristics.
Other attempts to incorporate transistors into textile fabrics have also been disclosed. For example, IEDM 2003 publication “Organic Transistors on Fiber”, by J. B. Lee and V. Subramanian, fabricates fiber transistors using textile technology. Based on the disclosed process, aluminum wires of 250 μm and 500 μm diameter were woven in a textile to form gate interconnects. A 150 nm to 200 nm low temperature oxide gate dielectric was deposited to encapsulate the gate. Source and drain contacts were patterned via orthogonal over-woven 50 μm diameter wires that served as channel masks and 100 nm gold was evaporated to form source/drain contact pads. After removing the over-woven fibers, arrays of transistors resulted similar to thin film transistors (“TFTs”), wherein each transistor was formed at every intersection. Although adequate electrical characteristics of the resulting fiber transistors have been reported for this fabrication method, such method is impractical for producing fibers on a large scale basis.
U.S. Pat. No. 6,856,715 B1, published 9 Nov. 2000, (Ebbesen, et al.), discloses an apparatus and a method for producing fabric-like electronic circuit patterns created by appropriately joining electronic elements via textile fabrication methods. The disclosed objective is to provide a lithography-free process to produce electronic and opto-electronic devices in sheet or fabric forms, or three dimensional structures that are different from traditional semiconductor processes. Further disclosed in this patent is the use of single component and multi-component fibers, wherein the components of the fibers can be arranged in different ways in the cross-section and/or along the axis of the fiber. Such fibers can possess various functionalities or combinations of functionalities, including electrical conductivity, semiconductivity, or optical conductivity, and can further include sensors or detectors activated by light, heat, chemicals, and electric or magnetic fields. The fibers may be bundled or braided. They can then be integrated into a fabric web pattern formation to obtain the desired functionality. Although this patent discloses an apparatus based on fiber and fabric predetermined forms and patterns, it does not disclose a way to fabricate the fibers so as to create the desired electronic and opto-electronic functionalities.
WO 03/023880 A2, published 20 Mar. 2003 (Neudecker, et al.), discloses fabricating multiple-layer and multi-function thin-film patterns, including solid-state thin-film batteries, on fibers. This application provides a method for non-contact deposition of functional layers, such as anodic, electrolytic, cathodic, electrically conductive, or semiconductor layers, on the surface of a fiber or portion of the fiber by means of shadow masking a vacuum coating process on a fibrous substrate. Although this process may lead to functional fibers, the process conditions and material deposition may severely affect the original fiber properties, with subsequent loss of characteristics required for textile processing.
U.S. Pat. Application 2005/0040374 A1, published 24 Feb. 2005 (Chittibabu et al.), discloses fabricating a photovoltaic cell from photovoltaic fibers. This application discloses a fiber core, which can be electrically insulating or electrically conductive. In the case of an insulating fiber core, an inner electrical conductor is disposed upon the surface of the fiber. This core is surrounded by a photoconversion material (which can include a photosensitive nanomatrix material and a charge carrier material), a catalytic media adjacent to the charge carrier material to facilitate charge transfer or current flow, and a light transmitting electrical conductor at the outer surface. In one embodiment, the photovoltaic fiber is formed by coating all materials onto the fiber core one after the other, while wrapping a strip of the light transmitting electrical conductor around the fiber in a helical pattern. Although this process may lead to functional fibers and may be suitable from a manufacturing point of view, material deposition over the fiber surface may severely affect the original fiber properties with subsequent loss of characteristics required for textile processing. Furthermore, the fiber must exhibit desirable thermal characteristics (i.e., a glass transition temperature of less than 300° C.). Also, with the layer-by-layer approach it can be difficult to achieve the desired durability and electrical performance in the final system.
Each of the above disclosures appears to achieve a desired functionality by post-processing a textile fiber via direct surface modification on the fiber surface. Such methods may fail to produce embedded electronic functionalities that are highly resistant to fracture during mechanical deformation, for example during bending or flexing as occurs in textile processing. In addition, none of the above disclosures appears to provide a fiber that can keep its original textile characteristics. Moreover, no disclosure appears to provide a fiber with elastic stretch and recovery properties. In this regard, the inability of a fiber to stretch and recover from stretch is a notable limitation in applications in which stretch and recovery properties are important (such as in many types of wearable articles and apparel). Furthermore, if integration of such functional fibers into the textile structure requires that the textile electronic functionality be rendered through the contacts provided by the functional fibers, the curved non-planar geometry of the fiber may not be the optimum for an acceptable electrical performance.
In view of the foregoing, it would be desirable to provide an energy activated textile yarn with planar active elements and mechanical properties that can be processed using traditional textile means to produce knitted, woven, or nonwoven fabrics.